1. Field of the Invention
The present invention relates to an exhaust gas cleaning apparatus and a method for manufacturing an exhaust gas cleaning apparatus for cleaning an exhaust gas emitted from a combustion engine.
2. Brief Description of Related Art
It is commonly known that combustion engines which are operated with fossil fuels emit pollutants. These pollutants comprise in particular so called particulates, e.g. soot particles, which are harmful to the human organism. As is further known these soot particles are emitted particularly by combustion engines operated with diesel fuel, which may be mainly found in commercial vehicles and increasingly in passenger vehicles.
In order to minimize the amount of these particulates, an exhaust gas cleaning apparatus, i.e. a so called particulate filter, is used, which is arranged in the exhaust gas duct of a combustion engine.
A conventional particulate filter is shown in FIG. 1. The particulate filter 1 is arranged in a body 3 made of metal, wherein the body is embedded in a fibre mat 4, and comprises layers of material, i.e. filtering walls 5 made of a porous filtering material which is permeable to the exhaust gas. As is indicated in FIG. 1 by arrows, the exhaust gas flows from the left hand side (entry side) to the right hand side (exit side) through the particulate filter 1.
The filtering walls 5 of the particulate filter 1 shown in FIG. 1 consist of layers of porous sintered metal or of ceramic material providing flow channels. By means of the stacked arrangement of the plates, there are exhaust gas flow channels 7 formed between these plates. These exhaust gas flow channels 7 are alternately closed at the entry side and open at the exit side, and open at the entry side and closed at the exit side, respectively, whereby the exhaust gas flowing into the exhaust gas flow channels 7 at the entry side is forced to pass through the porous filtering walls 5. The passing through of the exhaust gas is indicated by arrows 9 in FIG. 1. The filtering effect of the particulate filter 1 is based on the passing through of the exhaust gas through the filtering walls 5, whereby particles contained in the exhaust gas become trapped in the filtering walls.
It is a disadvantage of the conventional particulate filter that inhomogenous formation of deposits may occur, in particular at the end of exhaust gas channels which are closed at the exit side, and that an inhomogenous temperature profile in the particulate filter may occur, which leads to an inhomogenous regeneration of the particulate filter.
It is a further disadvantage that the manufacturing of a conventional particulate filter, having exhaust gas channels being alternately closed and open, is relatively difficult.